Functional amblyopia refers to a unilateral loss of visual acuity that is due neither to deficiencies in the optical components of the visual system nor to any apparent pathology within the visual pathways. Several lines of evidence are consistent with the prevalent viewpoint that the locus of the deficiency is cortical. Earlier electroretinographic and psychophysical research appeared to support this viewpoint in that no abnormalities of retinal function were detected. However for various methodological considerations, it is unlikely that such studies would have detected any abnormalities that may exist at retinal levels. Accordingly the aim of this project is to re-evaluate the integrity of retinal mechanisms in amblyopia through combined electroretinographic and psychophysical measurements of foveal function. The psychophysical experiments are aimed at determining whether the high spatial summation coefficients typical of the amblyopic fovea reflect greater physiological summation (e.g., enlarged receptive fields) or whether they are an artifact of failing to account for retinal inhomogeneity; i.e., for the scotomatous character of the amblyopic central field. Result to date have been more consistent with the latter rather than the former interpretation. Measurements of the photopic electroretinogram will be used to supplement the psychophysical measurements. Specifically, abnormalities in the electroretinogram recorded from the amblyopic eye would provide evidence consistent with the viewpoint that retinal mechanisms contribute to the amblyopic scotoma. The absence of any such abnormalities would, in contrast, provide evidence more consistent with the prevalent view that the locus of amblyopia is cortical.